Flexible device for encapsulating electronic components

ABSTRACT

A device for flexibly encasing electronic circuitry, where an electronic circuit is enclosed in a casing which includes a laminate consisting of metal and plastic sheets such as to form a diffusion impervious and electrically conductive structure which prevents harmful substances from reaching the electronic circuit and also prevents inductive electromagnetic exchange. Electrical conductors pass through the joint region of the laminate.

TECHNICAL FIELD

The present invention relates to a device for encapsulating electroniccomponents or circuitry such as to protect the electric circuit againstsubstances which may act deleteriously thereon, wherein the device alsoattenuates radiofrequency electromagnetic radiation so as to protect thecircuit against such radiation that can enter from the surroundings anddisturb the function of the circuit through induction, said device alsobeing active to protect the surroundings when the circuit concernedconstitutes a disturbance or interference source. The device includesthroughlet conductors which allow circuit-functional current and signalsto be applied when required.

TECHNICAL FIELD

It is often necessary to protect electronic circuits against differentinfluences emanating from the surroundings. Factors which influenceelectronic circuitry include water and other corrosive and electricallyconductive materia. It is also often important to protect the circuitryagainst electromagnetic radiation. In this regard, there istraditionally used different types of capsules which can be roughlydivided into two main groups, hermetic capsules and plastic capsules. Inthe case of hermetic capsules, the electronic circuitry is surrounded bya clean and dry volume of gas enclosed in a diffusion-impervious casing,normally a metal, glass or ceramic casing. When the casing is made ofmetal, glass throughlets are fused in the metal casing for leadingelectrical conductors between the encapsulated circuitry and the ambientsurroundings. When a plastic capsule is used, the circuitry issurrounded by plastic material instead of clean or pure gas. Althoughthe plastic material is permeable to water and gases, it willnevertheless often provide satisfactory protection, because coherentfilms are unable to form on the surfaces of the circuit components.Furthermore, plastic material has a more or less pronounced ability tobind chemically with the polar groups present in the surface of thecircuit components. These groups are thus blocked so as to be unable toform corrosion attack sites. The differences in the coefficient ofthermal expansion between the different materials present constitutes aproblem in both types of capsule. Another problem is that the circuitryis often so sensitive as to react against compounds which are split orcleaved from the actual encapsulating materials. A third problem is thatpolymeric material is often unable to withstand the working temperaturesconcerned, particularly as rises in temperature are often local,spotwise temperature increases, wherewith the plastic encapsulatingmaterials connect directly on to these points. This can result indegradation of properties and spalling of the corrosive substances. Inthe case of plastic capsules, it is often difficult to conduct heat awayfrom the electronic circuitry to the surroundings and they have noelectrically shielding ability. In addition to these technical problems,there is often a low price interest.

The levels of these various requirements vary, although they areparticularly stringent in the case of electronic circuitry for use incars and radio communication systems for instance. Several attempts havebeen made to glue hermetic metal and ceramic capsules, although it hasbeen found difficult to obtain glue joints which are age-resistant andimpervious. For the purpose of packaging electronic circuitry which issensitive to electric discharge caused by static electricity,encapsulating bags have been developed which include a casing comprisedof plastic sheets on which thin metal layers have been applied by vapourdeposition. These principles cannot be applied, however, in advancedencapsulation, since the metal layers obtained by vapour deposition orsputtering do not have a thickness which renders the encapsulationimpervious to diffusion. Furthermore, with regard to radio frequencyradiation, the depth of current penetration is many times greater thanthe depth of penetration in the case of a metal layer and consequentlythe resistivity in the casing is too high to attenuate such radiationeffectively and therewith provide an efficient shielding effect.

DISCLOSURE OF THE INVENTION

The object of the present invention is to avoid those problems whichexist with present-day electronic circuitry encapsulating devices. Inaccordance with the invention, there is provided to this end a device inwhich the electronic circuitry is encased, either completely orpartially, in a casing which is comprised of a plastic and metal-sheetlaminate. The metal sheet, or sheets, has/have a thickness at whichit/they is/are diffusion-impervious and electrically shielding, withregard to the necessary electrical conductivity and at the thenprevailing penetration depths of the electric currents at the frequencyconcerned, or corresponding rise times in the case of digitaltransmission. The device may include a laminate which comprises severalmetal sheets and intermediate plastic sheets, therewith providingextremely effective diffusion-impervious and shielding properties, whileobtaining a casing which is highly flexible and pliable, and enablingthe casing to be readily given a bag-like configuration. The casing isclosed and sealed with the aid of an adhesive, by thermal weldingtechniques, or by means of mechanical clamps. Electrical conductors arelaminated in one section of the casing sealing location in a manner toobtain an impervious join between the electric conductors and thelaminate. The bag is thus imperviously sealed by means of joints andelectric signals and electric current can be passed to the electroniccircuitry through the electrical conductors. The casing joints and thejoints between the casing and the electric conductors are constructed sothat the diffusion path between the plastic-metal laminate is so long,compared with the area in the plastic material which is perpendicular tothe diffusion direction, as to enable the amount of contaminants, forinstance water, that can diffuse into the bag during the lifetime of theelectronic circuitry to be ignored in relation to the volume of gasenclosed.

One advantage afforded by the invention is that the device provides apractically diffusion-impervious and electrically-shielded, inexpensiveencapsulation. Manufacturing costs are very low. Those parts of theelectronic circuitry which develop heat can be cooled by bringing theseparts into abutment with a large surface area on the inner surface ofthe casing and by applying cooling means to a corresponding surface areaon the outer surface of the casing, so as to carry away or transfer theheat generated. The metal sheets in the casing can be connected directlyto the electrical earth surfaces of the circuitry, so as to conduct awaythe induced currents in an electrically shielding function. Thecomposition of the gas enclosed together with the circuitry can bechecked in conjunction with sealing the casing, and the gas volume canbe analyzed at any desired time, for instance with the aid of amasspectrometer, with the intention of checking the concentration ofcontaminants in the casing, for instance water. A gas sample can betaken through a very small opening in the casing, which is thenpreferably resealed, for instance in the same way as the remainingcasing joints were achieved. When required, other devices may beincorporated in the casing for carrying light or heat, for instance.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of a flexible device for encapsulatingelectronic circuitry in accordance with the present invention.

FIG. 2 is an enlarged, sectional view of one corner of the inventiveencapsulating bag.

BEST MODE OF CARRYING OUT THE INVENTION

FIG. 1 illustrates a typical device for flexibly encapsulatingelectronic circuitry. The device includes an electronic circuit board 1which is fully enclosed by a bag 2. The bag 2 is sealed, for instance,by fusion-welded joints in the joint region 4. Electrical connectionsare achieved with the aid of electrical conductors 3 sealingly embracedin a part of the joint region 4.

FIG. 2 illustrates part of the device in larger scale. The bag iscomprised of a laminate structure 2 consisting of metal sheets laminatedbetween plastic sheets 5 in a manner such that the plastic sheets 5adhere sealingly to the whole of the surfaces of the metal sheets 6. Thelaminate structure 2 from which the bag is made is closed sealingly inthe joint regions 4. The metal sheets 6 form a diffusion barrier againstlow molecular substances that are liable to damage the electroniccircuit board. It is highly improbable that any damaged areas and pores7, 8 in the metal sheets 6 will lie close together in the laminatestructure 2. When seen in relation to the area extending perpendicularlyto the diffusion direction, the diffusion paths of the penetratingcontaminants in the laminate structure 2 and the joint region 4 are verylong, and also in those points in the laminate structure 2 where defectsin the form of pores 7, 8 in the metal sheets 6 are located. As will beunderstood, the length of the diffusion paths in relation to the area atright angles to the diffusion direction and also the thickness of thelaminate structure 2 have been greatly exaggerated in the Figure, forthe sake of illustration. In the illustrated embodiment, the laminate 2is comprised of the following sheets, as seen from the outer surface ofthe casing: Polyethylene terephthalate 0.023 mm, aluminium 0.014 mm,polyethylene terephthalate 0.023 mm and, furthest in, low-pressurepolyethylene 0.075 mm. The casing joints are formed by fusing thelow-pressure polyethylene sheets together at a temperature of 150° C.and a pressure of 100N/cm².

According to another embodiment, certain parts of the casing areadvantageously joined to metal parts, for instance to carry away heat,or to a glass window through which a display on the electronic board canbe seen. According to a further variant of the inventive device, a jointis advantageously formed between the electronic circuit card and thecasing. In those instances where joints are desired with other materialsthan the actual laminate 2, for instance with metal, glass or withcircuit board surfaces, that side of the laminate 2 which is to beheat-welded to these materials is comprised of polyethylene which hasbeen modified with carboxyl groups which have been cross-linked withzinc ions, so-called ionomer plastic. Such plastics have the ability toform bonds with many different types of surfaces, so as to obtain ajoint of satisfactory mechanical strength. In these cases, the fusionwelding process can be effected at 130° C. and at 100N/cm².

It will be understood that other variants are conceivable, these furthervariants being limited solely by the scope of the following Claims.

I claim:
 1. A device for flexibly encasing an electronic circuit toprevent the electronic circuit from coming into contact with harmfulsubstances present in the ambient environment, and for preventingundesirable exchange with induced electromagnetic fields, comprising animpervious casing comprising a metal and plastic laminate, and whereinthe metal has a thickness which renders the laminate impervious todiffusion and capable of attenuating electromagnetic, radiofrequencyradiation, and wherein the laminate has integrated therein electricconductors in the form of conductive paths printed in the metal andwhich can be electrically connected to the electronic circuit.
 2. Adevice according to claim 1, wherein the laminate and the electricconductors are each connected to a respective joint region by fusionwelding.
 3. A device according to claim 1, wherein the laminate and theelectric conductors are glued to their respective joint regions.
 4. Adevice according to claim 1, wherein the laminate and the electricconductors are mechanically clamped to their respective joint regions.5. A device according to claim 1, wherein a part of the casing is joinedto a material other than the laminate.
 6. A device according to claim 1,wherein a part of the casing is joined to the electronic circuit.